1. Field of the Invention
The present invention relates to an image display device and method, and to an image communication apparatus and method.
2. Description of the Related Art
As a result of diffusion of computer networks such as Internet, it is becoming practically possible to transmit even image data on a computer network, although some problems still exist in resolution, the transmission rate and the like.
In the general configuration of an image data base, an image file server and a client are connected to a network, and the image file server transmits assigned image data to the client in response to a request from the client. By interactively operating a computer, serving as the client, the user can display an arbitrary image stored in the image file server on a monitor of the computer.
For example, as shown in FIG. 1, a summary of image data stored in an image file server is displayed on a client's monitoring picture surface. In FIG. 1, reference numerals 20-28 represent schematic images for displaying an outline of the image data stored in the image file server. By selecting one of the displayed schematic images 20-28, the user selects a desired image data.
The schematic images 20-28 are subjected to hierarchical encoding, for example, according to a JBIG (Joint Bi-level Image Group) method which is an international standard encoding method. Since hierarchical encoding can decode a plurality of images having different resolutions from one image data, it is suitable for a use in which it is intended to decode a plurality of images having different resolutions. Conventionally, in order to display schematic images on a client's monitoring picture surface) hierarchically encoded image data is decoded in accordance with the resolution of the picture surface.
The band of a computer network greatly changes in accordance with a change in the state of use of other users, the configuration of the network (for example, switching from a wire LAN (local area network) to a radio LAN), or the like. Since preparation of means for securing a necessary band width is insufficient, it is generally impossible to secure the necessary band width.
When the band is narrowed as a result of a change in the band width as described above, the response time may, in some cases, extremely increase due to a decrease in the transfer rate of encoded data, so that it is necessary to wait for a long time for displaying schematic images.